WATER FOR INDUSTRIAL PURPOSES Lime, CaO ..... Magnesia, MgO .... Sulphur trioxide, SO3 . Chlorine, Cl Nitric anhydride, NaO5 Nitrous anhydride, N2O3 Ammonia, NH3 .... Solid residue at 180° . Total hardness, in French degrees Organic matter (oxygen consumed) PIT 100 litres. up to 12 grams 4 ,, O'2 ...... vIO ,, o o 10-50 lip to 32 up to o'.> As is seen from this table, to be potable a water should first be quite free from ammonia and nitrites, and should contain only small proportions of nitrates and chlorine and a very small amount of organic matter (expressed as oxygen absorbed). These substances arc mainly considered because, although they are quite harmless in the small proportions in which they always occur in water, their presence demonstrates that the water was formerly or is still contaminated by organic matter (sewage water, drainings from inhabited districts, etc.). A water containing ammonia or nitrites or organic matter (beyond the limiting amount) should always be rejected. A water containing nitrates or chlorine beyond the established limits should be suspected, unless it can be proved definitely that these salts come from the soil The presence of phosphoric acid is also a sign of the organic contamination of water. In special rases as much as 5-0 grams of chlorine per 100 litres may be tolerated, so long as the water exhibits no other defect. Table II gives the compositions of the water supplies oC various towns. WATER FOR INDUSTRIAL PURPOSES Waters for use in industries, for steam boilers, laundries, factories of different kinds, are examined especially with reference to their content of lime and magnesium salts. With such waters it is required to know the content of lime, magnesia, sulphuric acid, and airborne acid. Further, the quantities of lime and sodium carbonate necessary to correct any exces- sive hardness of the waters must be known. The addition of lime is neces- sary to transform the calcium bicarbonate into carbonate, to saturate the free carbonic acid and to precipitate the organic matter ; that of soda is required to decompose the calcium sulphate. To eliminate the latter and sulphates in general, barium chloride may also be used. In practice use has been made and is still made, of the results of the hardness determination (sea Potable Waters : Partial Analysis, 2), but this test gives only approximate and sometimes unexpected results, since it furnishes no information concerning the relation between lime and mag- nesia, or between carbonates and sulphates. To obtain reliable, data it is necessary to carry out—besides various qualitative tests to ascertain if the water is more or less rich in lime, magnesia, carbonates, sulphates, or chlorides—the different determinations indicated for potable waters (see Potable Waters, Complete Analysis, a, 3,4, cj and 10), or at least the following tests suggested by Lunge x and recognised as of technical value. 1. Volumetric Estimation of the Total Alkalinity .—Two hundred c.c. of the water are titrated in the cold with N/5-hydrochloric acid in pres- Lunge, Technical Methods ol Chemical Analysis (London, 1908), Vol. I. p. 800.